This Is Very Embarrassing

Over Labor Day weekend we took a trip to the beach with another family. Both of us have older children who are friends so they were all with us too.
One morning everyone had gone down to the beach while I stayed behind to clean up from breakfast. When their son who is 19 returned to get his sunglasses he had forgotten we struck up a conversation.
I had just changed into my bikini and it was obvious he was flirting.
I was standing behind the sofa watching the news on tv when he walked up behind me real close kissing me on the neck. I started to move but he pinned me to the back of the sofa.
I had actually been attracted to him so when he kissed me on the neck again I didn’t say anything. Then he ran his hand between my legs and I told him it needed to stop.
Instead I could tell he was getting himself out then he pulled my bikini crotch aside bent me forward and went inside me.
I just said oh my god and relaxed telling him it was ok but asking him to not cum in me because I wasn’t on birth control.
I’d be lying if I said I wasn’t enjoying it but then he shoved deep stopping and I yelled no no no but he finished inside me.
Once he had finished I ran to the bathroom and cleaned up best I could.
I asked him if he would go to a store and get me a plan b. He said he would later when the others wouldn’t suspect anything. That never happened and I didn’t have a chance either.
My period was due on the 17th so I was 12 days late as of yesterday. After my husband went to work this morning I got a pregnancy test which confirmed what I already knew that I’m knocked up.
My husband and I use condoms for birth control so I can’t be one hundred percent certain who the father is but odds are it’s their son’s.
I’ll just have to keep it a secret and hope that nothing happens to expose my infidelity.