Hi @Cupcakesaregood - I remember your previous thread well (it was very recent) and am going to use some knowledge that I gleaned from that in responding to your new post. Hope that's not a breach of MN etiquette.
I really feel for you. You are in a deeply painful situation which you are - understandably - struggling to come to terms with and work out what to do next. Based on what you said before (feel free to correct me), you had been married a year when you discovered an unplanned pregnancy six months or so into the pregnancy so you had only a few months to adjust to the arrival of your DC. Shortly after discovering you were pregnant, you discovered that your DH appeared to be having an EA with another woman. Your DH agreed to give her up and apparently deleted her number from your phone. Fast forward a few more years and, as you say, you are intentionally pregnant with no. 2 and it turns out that DH has kept her tel no. You say he has not been in touch with her during the last 3 years - presumably that is what he is telling you - but as I recall from your previous thread the position was somewhat unclear about that. The real point, though, is that your marriage is an unhappy one. It's been unhappy ever since you discovered the EA which means that - roughly speaking - for 75% of the time you have been married, your marriage has been an unhappy one. And perhaps it's been unhappy for your DH from the outset given that he was having an EA within the first year of your marriage, if not earlier.
If I have understood the situation correctly, the very painful difficulty you face - through no fault of your own - is that you are trying to build a family life with a man who is not emotionally committed to you and is hankering after another woman or at least is hankering after the freedom to pursue other relationships. It may be that without the unexpected arrival of DC1, your DH would already have ended your marriage and gone to be with OW. Or maybe not. But as you pointed out yourself in your previous thread, he was already having an EA within the first year of your marriage (perhaps before that) and that can only be a bad sign - looking elsewhere in the first year of marriage shows he was already not equal to the commitment which he had taken on by getting married.
You don't mention your age (I can't remember if it came up in the previous thread) but I'm guessing you're still young (20s/30s). You most likely have several decades of life ahead of you. Don't you deserve better than to spend those decades in an unhappy marriage with someone who you know, deep down, isn't able to commit to you emotionally in the way a marriage partner should and who will probably leave you when your DC are grown if not before then? It can surely only be bad for your emotional and indeed mental health. It is also not a good relationship model for your DC who might grow up to replicate it themselves and think that an unhappy marriage is the norm. Don't you deserve to be free to find someone who does love you and wants to be fully committed to you emotionally? Of course, no-one can guarantee that you will meet such a person but the chances are high that you will. I know a number of people who have made very contented second marriages after extremely painful experiences with their first.
It would at any time be very hard to face the fact that your DH doesn't care for you as he should and it is particularly hard to do when you're parenting a toddler and pregnant with no. 2. You're in a vulnerable and dependent position. But the end of your marriage - if that is what happens - doesn't have to mean the end of co-parenting. From what you've said, your DH is committed to your DC and you may well be able to build a very successful co-parenting relationship which could in turn be a great model for your DC.
It's not a foregone conclusion that your marriage has to end but it is hard to see how you can turn a marriage which has been unhappy for the vast majority of the short time you have been together into a happy one, and that is what you deserve.
Thinking of you, OP.