I'm still having fun wading through the old 1928 Danta De hymnal, and its fun time playing with public domain Irish stuff that went back a century or several centuries.

As you can tell from the subject line, the simplification by law of Irish Gaelic spelling had some fairly hardhitting effects on the title of this hymn. (You'll also see a lot of "sg" sounds being currently spelled "sc" in Irish. Same thing, really.) "A Iosa" has also turned into plain old Iosa, however. That's either singers not understanding the vocative they hardly could hear, or arrangers deciding they wanted the whole thing shoved into the third person. Or maybe everybody knows it's there and feels no need to spell it out. Shrug. It's also worth knowing that "dilis/dhilis", which usually is translated in love songs as "dear", actually means "solid, faithful, loyal".

The Danta De hymnal tune is "The Star", which is a nice old traditional tune. You can hear it in a barebones version at my site, or in a much nicer version on Kevin Cawley's Danta De site.

Somebody else set this public domain poem to an entirely different nice old tune (probably Sean O Riada, for his Ceol an Aifreann book of Irish language mass music). This is the tune that you hear on recordings, such as the recent one on the album Harmony by The Priests. This also seems to be the tune listed as "BI IOSA IM CHROISE" in some places.

Here's my translation (one of zillions), with the original verses under them. The one really important thing is that the old version has "mar an gceadn' " in the final verse, which means "likewise". Everybody later heard this as "mar an gceann", which would make it all about your head, and is reasonable Irish poetry. So my translation pretty much only works with the old version of the song and the old setting to "The Star".

Be, o Jesus, in my heart, And each hour, be recalled.
Be, o Jesus, in my heart, For repentance when I fall.
Be, o Jesus, in my heart, Be my companion constantly;
So, o Jesus, faithful God, Oh never, never part from me.

Without Jesus, all my thoughts Are unpleasant ones for me.
Without Jesus, all I write Dies in my mouth silently.
Without Jesus, all I do Does nothing good in life, I find.
So, o Jesus, faithful God, Go both before me and behind.

He is Jesus, my dear King, My beloved and my friend.
He is Jesus, my defense; Sin and death -- He makes them end.
He is Jesus, my delight, Mirror to show me my true face.
So, o Jesus, faithful God, Oh never leave me; I need grace.

Be, o Jesus, evermore In my mouth and in my heart.
Be, o Jesus, evermore Also in my mind and thought.
Be, o Jesus, evermore In all I learn and all I'm shown.
So, o Jesus, faithful God, Oh do not leave me here alone.

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Bí, a Íosa, im' chroídh-se i gcuimhne gach uair,
Bí, a Íosa, im' chroídh-se le h-aithrighe go luath,
Bí, a Íosa, im' chroídh-se le cumann go buan,
ó, a Íosa, 'Dhé dhílis, ná sgar, Thusa, uaim.

Gan Íosa mo smuainte ní thaithnigheann liom féin,
Gan Íosa mo sgríbhinn, no foghar mo bhéil;
Gan Íosa mo ghníomha ní maith in san tsaoghal,
ó, a Íosa, 'Dhé dhílis, bí romham is am dhéidh.

'Sé Íosa mo Rí-se, mo Chara is mo ghrádh;
'Sé Íosa mo dhídean ar pheacaidh is ar bhás,
'Sé Íosa mo aoibhneas, mo sgáthán do ghnáth,
A's, a Íosa, 'Dhé dhilis, ná sgar uaim go bráth.

Bí, a Íosa, go síorraídhe im' chroídh-se is im' bhéal,
Bí, a Íosa, go síorraídhe im' thuigse mar an gcéadn',
Bí, a Íosa, go síorraídhe im' mheabhair mar léigheann,
ó, a Íosa, 'Dhé dhílis, ná fág mé liom féin.