I dont know what to do if anything...Please help? (concerning possible infidelity)?

I've known a couple for years. I knew them even before they were dating. There was a long time about 5 years or so that we didn't have any contact with each other. But recently I've come back into contact with this couple. I like the wife. She's nice and we have friendly conversations. The husband I know more and we've spent a lot more time together...but were hardly ever alone. We have the same circle of friends but the wife is hardly there when we (the husband and I) and our friends all hang out. But recently i've felt that there might be something more. For different reasons the husband will try to use excuses the touch my hair or hands. He'll occasionally flirt with me but in a subtle, playful way. Or call me "sweetheart" or use a nickname that only he has ever called me. I don't want to start a relationship with him. Im not really interested in him except for friendship and seeing him as an older brother. But i don't know if im imaging things(when it comes to relationships im pretty oblivious) Or if he really does like me more than just a friend. He is my type but he's married so that crosses him off my list. It hasn't been unbearably awkward but these past couple of weeks it feel like things might get more intense. He's even done the things i mentioned above right in font of his wife. basically what im asking is if he 1) does like me or am i being stupid and 2) if he does like me what am i supposed to do. im not really a confortational person. Help please I cant really ask people i know because we all know each other! Thank you soooo much!!!