Casey, is he single and available? If not, you must leave him alone and never associate with him again. By the way getting involved with someone at work is not a good idea but a little late now. It becomes awkward when things don’t work out.
If he is single and available one of two things. Girl, you are 26 and have time on your side. He’s lucky to get a young, vivacious girl such as yourself, please do not be desperate. When you’re 36 he’ll be 52! Put in only as much effort as he is putting in, if he withdraws, you withdraw also. Don’t be too available and needy as you say you’re the one doing the initiating, let him chase you. Give him time to miss you and wonder why you’re not chasing him as usual. When you do spend time with him make sure it’s enjoyable for him, be happy and positive so when you’re not with him he misses you.
Secondly, yes maybe he is using you for sex. Listen to your gut instinct, it’s usually right. He’s 42, maybe he doesn’t see much of a future with you because of the age gap..maybe you two are at different points in your lives? Maybe you have different values. Does he have kids? Maybe he doesn’t want anymore but you’re young and might want children one day. There’s endless reasons why he might not be taking you seriously or think you two are compatible. Men can have sex and not get attached.
If you like him a lot, be patient, give it a little more time to see if his attitude towards you changes. Tell him how you feel if you think the time is right, of course not too soon you might scare him off. If you don’t see it moving towards something more meaningful in say a month or two then cut your losses, move on and find someone who’ll adore you as much as you do him. It will be his lost, move on! If you keep letting him use you for sex you’ll end up feeling awful and cheap, not worth it.