I’ve Gotten Myself In A Horrible Predicament

I’m 31, married with two kids. My husband is out of town working many times for as much as six weeks.
The last week of January my boss and I had a dinner meeting with a client where we had a bottle of wine then a couple more drinks in the lounge afterwards.
My boss is a very handsome guy in his mid-40’s who I have worked for for almost six years. He is also married with kids.
I had never given a thought that he had any feelings for me and I certainly had never considered him anything but my boss.
However, that evening after having the wine and drinks when he expressed how he felt about me I let myself make a poor decision.
We ended up at a motel after he had stopped to buy condoms since I told him I wasn’t on birth control.
The sex with him was exciting, long lasting and very intense.
However, when I could tell he was nutting I pushed hard to get him deep inside me and the condom broke so I got his full load.
Afterwards we drove back where he bought me a Plan B which I took later that evening. My period was due in nine days so I thought nothing more about it.
When my period was due last week it didn’t come. I waited several days hoping I was just late but then took a pregnancy test and I am pregnant. Of course there’s no doubt whose it is since my husband has not been home for over a month.
I am very pro-life so an abortion is out of the question. I will have no option but to tell my husband I was unfaithful but don’t plan to tell him who with. I’m not sure how my boss will react when I tell him since we took every precaution to avoid this situation.
This is a terrible prediction to be in since I’m sure my husband will probably want a divorce and my boss being married will probably help me but not want to loose his marriage.