I (32 F) found out my husband (41 M) has been sending money to another woman. What do I do now?

I apologize if wording seems vague in some Places. My OP was taken down by a bot for sounding like a request for funding.

I (32f) have been with my husband (41m) for 7 years. While filing our taxes I needed to reset our password, linked to his email. I went into his inbox to retrieve the link and it’s in an “updates” category just above a completed a request for money to a woman I don’t know. In what is a violation of his privacy, I searched his inbox for the platform he used to complete the transaction and found that over the past month he has sent more than three thousand dollars to this same woman. We keep our finances separate so I had no idea this was happening. He had asked if i could contribute to some larger expenses but had what seemed like legitimate excuses “stepson needs money for his spring break trip.” “MIL (who has lupus) needs help to cover the cost of a specialist visit” etc. I can see the exact amounts I sent him funneled almost immediately to this woman. There has been no change to his routine, no unexplained nights out, no unusual phone calls, no change in behavior at all except him secretly sending this money. My question is, what do I do now? He’s already proven he is a liar so I don’t know if three is any point in asking him directly. Do I check his phone to see if there is any other evidence of an affair? Do I just ask for a separation? I’m totally lost and am an orphaned only child so I have no one to ask for advice in “real life” and have never dealt with a cheating partner. The craziest part is that he has seems absolutely normal at home. Absolutely no change in behavior that would indicate anything out of the ordinary is happening and now I’m wondering what other secrets our seemingly happy marriage might be hiding.