My boyfriend(22M) constantly is in contact with best friend’s widow(20F)

We’ve been dating for 5 months or so and it picked up really quickly. For some context, he’s in the military and Im in school. We really hit it off in the first 2 months, hanging out every weekend and going on trips. We both said “I love you” within the first month or so. He’s the first person I’ve fell in love with. We constantly Talked about our future together and marriage. I’m starting to question our relationship and here’s why. For some context: During a week in June, he went back to his hometown. He had been planning this lake trip with his close group of hometown friends for a while. He ended up inviting a friend(20f) of his, that recently lost her husband(one of his best friends), to the lake trip as well. His best friend passed late last year and my bf’s been helping his widow ever since then. When we initially started dating I noticed that he would always answer her fts and text pretty frequently. One time he even answered a ft right after we just had s*x. It disturbed me a lot but I brushed it off because he is very sweet and attentive so I thought it was a quick lapse in judgement. During these fts she would show off her outfit, ask opinions on them, talk about her day/drama, etc. I’ve never done that with a platonic male friend but he reassured me that she was just going through a rough time and needed someone. Whenever I was mentioned or in the ft call her tone would change. Now this all happened before the lake trip. During this lake trip she ends up talking to him privately and saying she has feelings for him. She said and I quote “I’ve been dropping so many hints and I have really strong feelings for you”. He said that nothing happened and he told her that he was in a happy committed relationship. I had to pry this out of him. He didn’t own up to leading her on or understand the impact of his actions. Instead he said that he just saw the FaceTimes, emotionally support, and texts as him helping his best friends legacy. We’ve discussed this a couple times but I never feel at peace with the situation. This situation and some other issues have caused a lot of arguing. Any suggestions or advice on how to resolve this? Would this be considered cheating?

Thanks