If adequate is all you've got don't have kids with them. Honestly. Do it single with a sperm donor if you have to but do not tie yourself to an "adequate" man or someone you hope will improve for the sake of the baby.
They won't, which means eventually you'll get so fed up that it's likely you'll split. Trust me, this is not simply "Ah well I'll do it on my own then" - I thought that. Bear in mind -
If "adequate" means that you can't really trust him to do things properly, that means you end up having to hand over the most vulnerable and important person in your life to someone that you can't trust to look after them properly.
If "adequate" means that you can't really rely on them that means you have to find the words to deal with your DC's disappointment when Daddy lets them down again. Or explain to them when they are older why he didn't stick around or favours his new family over them.
If "adequate" means that they are not the role model you would hope for, you will have to deal with watching DC grow up and emulate the role model that he is, not the one you'd hope he would be.
Babies don't really bring you together so much as they test the strength of your relationship. It's like if you had a footbridge you were always nervous about crossing because you didn't know how strong it was and sometimes it seemed a bit flimsy, and then one day somebody leads a herd of elephants over it, and it's fine. Your confidence in the bridge would shoot right up and you'd never worry about it carrying your own weight again. (This looks like "it brought us closer together") But it didn't actually get any stronger, it had to be that strong from the start. The bridge is a relationship and the herd of elephants is the baby - a weak bridge and even an average bridge would collapse under the weight.