I have a feeling that you suspect your boyfriend because you don't trust yourself.
But just how far did you go when 'contacted' by your ex?
You need to have some contact with him so that you can raise your shared child well.
If you met to drop off/pick up the child and he was pleading, and you let him for far too long and even got into some serious touching, then you need to sit down with yourself and decide what exactly it is you want. Stop suspecting someone who shows no evidence of cheating and fix your own trustworthyness.