A 7 month affair so soon after marriage is not merely an expression of weakness but that there is something fundamentally wrong with the relationship.
In order to be able to stay in the marriage you have needed to demonise the OW as 'evil', to exonerate your H. This a falsification of what occurred. However crazy you now believe her to be, he is as responsible as she. He was not a victim, he was a cheat.
Putting all the blame on the OW implies that you do fundamentally believe that infidelity breaks a relationship, and the only way to preserve it is to alter the facts.
Deceiving yourself is a dangerous strategy, and you must be prepared for the narrative you have created to fall apart.
There is difference between excusing your H and him actually repenting sincerely and redeeming himself.
You will be stuck in a situation where your conscious mind has chosen to forgive him, but in your heart you know that he has not fulfilled the conditions required for a genuine & thorough forgiveness.
You will be in constant conflict now between what you choose to believe, and what you know to be true.
You will thus fear further transgressions, and continue to be angry with him, not just for his affair, but because he is still behaving badly, and because he is, fundamentally, not the man you thought you had married.
It makes a great deal of sense to hear that your mother put up with multiple infidelities. You have learnt coping strategies for infidelities from her, whereby infidelity is not a deal breaker but something to be assimilated. And you have apparently inherited low expectations of men.
So the rows will continue, they will worsen after you give birth, and you will either a) put the baby first & get so furious with him that you end up chucking him out or b) he will be unfaithful again to put an end to the exhausting conflict. Or both.
A man who does not stop rowing with a woman because she is pregnant, and he is a decent person, is not going to stop simply because you say 'cheese'.