Almost 50 years old and have to ask this question?

All I ask is if you answer honestly and have been a long term relationship and nothing mean.

I have been in a relationship with my boyfriend for 5 years. We do live together for a little over a year. Lately he has been in bad moods over work or maybe something else is going on that he is hiding. I get it I’ve been there. But I feel in my gut he is either interested in another women or just losing interest in me. I want to have a conversation about it but want it to be adult and honest Any tips on how to start the conversation?
Almost 50 years old and have to ask this question?
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