Hi, there seems to be some conflict in the various places I checked. Some sources say that Mo Mhuinín Bán is a different song, sung in Munster, as opposed to Fath Mo Bhuartha, sung in the west of Ireland. The tunes are acknowledged to be similar, however. This is what I pulled off of Mudcat:
MO MHUIRNIN BAN ('Sé fath mo bhuartha)
'Sé fath mo bhuardhartha, nach bhfaighim cead suaimhnis
Ins an ghleanntán uaigneach seo a mbíonn mo ghrádh.
Tig im ar uachtar ann 's mil ar luachair
'S le méith na huaire 'bíos na tortha ’ fás.
Ní bhíonn gaoth tuaidh ann ná sneachta buan;
Tá caladh is cuan ann ag loing ‘s ag bád.
Tá tuilleadh buaidh’ air, níl doirse cruaidhe ann,
Dá ndéantá suas le do Mhuirnín Bán
Ní ar shliabh na ar fhraochlach atá mo mhian-sa
Ach ar thalta mine, a dtig meas is bláth.
Tá an chuach ag glaoidh ann i mbárra craobh ann;
Tá an eorna bhuidhe ann ‘s a’ coirce bán;
Tá an loch is aoibhne ann, a dtig bric 'na scaoith ann;
Tá an fiadh 'na luighe ann ‘s an eala a’ snámh;
Tá an bheach is críonna ann 's a háras díonta
'S tá mil 'a taomadh ar mo Mhuirnín Bán
Agus shíl mé, ’ stóirín tá aoibhiúil óg deas,
Go déanfá foghluim ar éalódh liom;
'S nach bhfuil tráthnóna nó maidin reoite
Nach tú an réalt eolais a bhí 'gabhail romham,
Ag siúl na mboíthre 's na gcoillte ró-ghlas,
Ní bheadh orm brón ná tuirse croidhe;
Ach mé bheith pósta ar bhláth na hóige
'S í ’ siúl go státúil le mo thaoibh.
Summary translation
The cause of my sorrow is that I get no quietude in this lonely hollow where my love dwells. It is fertile and temperate [There is butter, cream , honey and fruit there, no north wind or lasting snow, there’s a port and harbour for ships,] and it would be better yet if you were reconciled with your fair-haired darling.
My love’s not on the hillside but in the fertile plain. There one finds the cuckoo calling at the top of the branches, barley, oats, a fine lough full of trout, deer, the swan, the wise bee and honey in abundance for my fair-haired darling.
I thought, lovely young sweetheart, you’d learn to elope with me and that you’d be my star of knowledge morning and eve. Were I married to the flower of youth and she stately by my side, I’d never be sorrowful.
============================================
X:1
T:MO MHUIRNIN BAN
N:From the book P Mac Seáin, Ceolta Theilinn (Belfast: Institute of Irish Studies at Queen’s Univerity, 1973)
N:A version of 'S é fath mo bhuartha collected in Teelin, Co Donegal by Pádraig Mac Seáin
I:abc2nwc
M:3/4
L:1/8
K: D
z2(A G) F E|D2F A d e/2 c/2|(d B) A2F/2 G/2 A G/2 F/2|
w:'Sé_ fath mo bhuardhar-tha, nach bhfaighim cead_ suaimh_-nis In-sa ghleann-tán_
F3/2 E/2 D E D D|D4(A G) F E|D D F A d (d/2 B/2)|
w:uaig-neach seo a mbíonn mo ghrádh.Tig_ im ar uach-tar ann is mil ar_
(d B) A2F/2 G/2 A F/2 E/2|F3/2 E/2 D E D/2 D3/2|D4A A B c|
w:lua_-chair’S le méith na_ huai-re 'bíos na tor-tha 'fás. Ní bhíonn gaoth_
d2e d (3cAB|(=c2d2)e (3ddc|A2G E D D|
w:Tá ca-ladh is cuan ann ag loing ‘s~ag
E4A G F E|D2F A d e/2 c/2|(d B) A2|
w:bád. Tá_ tui-lleadh buaidh’ air, níl doir-se_ cruaidhe_ ann,
F/2 G/2 A F E|F E D E D D|D4z2
w:Dá_ ndéan-tá_ su-as le do Mhuir-nín Bán
==================================
'SÉ FATH MO BHUARTHA
Sé fáth mo bhuartha nach bhfaighaim cead cuarta
Sa ngleanntán uaigneach ina mbíonn mo ghrá;
Bíonn mil ar luachair ann is im ar uachtar
Is i dtús an fhómhair a bhíonn na crainn faoi bhláth.
Níl gaoith aduaidh ann, níl sneachta buan ann;
Tá caladh is cuan ann ag loing 's ag bád;
Tá tuilleadh bua ann, 's níl tuaras na Cruaiche ann,
An té a dhéanfá suas lena mhuirnín bán.
Agus shíl mé a stóirín, nuair a bhí tú óg deas,
Go ndéanfá foghlaim ar éalú liom;
Is nach bhfuil tráthnóna ná maidin Domhnaigh,
Nach tú an réalt eolais a bhí ag gabháil romham.
Ag siúl na móinte is na coillte clómhar,
Ach mé bheith pósta le mo mhíle stóirín,
Is mo lámh go bródúil ar a brollach mín.
===================================
X:2
T:IS É FATH MO BHUARTHA
Q:1/4=80
I:abc2nwc
M:3/4
L:1/8
K: D
A/2G/2F ED- DF|Ad ed AF-|F2GA FE|EF ED DD-|
DA/2G/2 FE D2|FA de dA|F3G AF|E2FE DD|
D2FG AB/2c/2|d2ed c/2A/2B|=c2de d^c|A2GE DD|
E2A/2G/2F ED-|DF Ad ed|AF- F2GA|FE- EF ED|DD- D zz2|]
===============================
X:1
T:S E FATH MO BHUARTHA
N:'S é Fáth mo Bhuartha: “Ar Ceól Féinig” (published by Longman, Brown and
N:Nolan); Mrs Eibhlín Costello, “Amhráin Mhuighe Seola” (different tune, words
N:titled ‘A Mhuirnín Bán’); “Abair Amhrán” (lyrics only, published by
N:Comhaltas Uladh)
I:Cuisie an Cheoil Dublin Dept of Educ. 1976
L:1/8
K: D
z4A/2 G/2 F3/2 E/2|D2F3/2 A/2 d e|
w:Sé fáth mo bhuar-tha nach bhfaighaim cead
(d/2 A/2) F2G/2 G/2 A F|E2F3/2 E/2 D3/2 D/2|
w:cuart-a_Ar an ngleann-tán uaig-neach na mbíonn mo
E3(A/2 G/2) F E|D2F A d3/2 e/2|
w:ghrá;Bíonn mil_ ar lua-chair ann im is
(d A) F3/2 G/2 A F|E2F3/2 E/2 D3/2 D/2|
w:uach-tar_'Sgo tús an fhuaicht bíonn na crainn faoi
D3A (3(AB)c|d (e e) d (3(=cA)B|
w:bhláth.Níl gaoith a_-duaidh ann, níl_ sneacht-a_
=c (d d) e d ^c|A2G E D3/2 D/2|
w:crua ann;Tá_ caladh’s cuan ann ag loing 'sag
E3(A/2 G/2) F E|D2F A d/2 d e/2|
w: bád;Tá tuill-eadh_ bua ann, 's níl tu-ras na
(d A) F3/2 G/2 A F|E2F3/2 E/2 D D|D3
w:Cruai-che_ ann,Da ndéan-fá suas le do mhui-rnín bán.
=======================================
Ceolta Gael gives the last four lines of the second verse as
Ag siul na mbanta is na gcoillte cnomhar
ni bheadh orm bron no duibheagan croi
ach me bheith posta ar mo mhile stoirin
is mo lamh go broduil ar a brollach min
=======================================
This lot ought to keep you off the streets for a few hours. 
Hope that helps,
djm
