Looking for PI service

I am looking for a PI service to follow my boyfriend and figure out where he works when it's not for his business.

We've been dating for 2 years and he said he's going to propose once ge has enough money for a ring. I told him that there are other cheaper options that I would prefer over diamonds, but he was insistent that I "get the best ring". He owns a cleaning business and he has a second job as a waiter in a Mexican restaurant. He has been working at that restaurant for about 6 months and because I am so busy with my own work schedule I never had the opportunity to visit the restaurant. But one day I was able to go with my friends right after work. He told me that he was working and I just wanted to surprise him. But when I got there, and when I asked if I could see him, the manager said that no one by that name has worked there.I almost always know when he's working for his business because I set up those appointments for him, and he also posts it on his business Instagram.

I now have suspicions that he could be cheating on me with his one of his workers because he is very "friendly" with them. I never suspected anything before because I dated and known other men who have a very flirtatious personality but are very loyal to their partner. But this is the first time that someone with his personality has legitimately lied to me, and when I look back, he's fairly insistent on getting a ring that he knows that I don't necessarily prefer.

Is there a private investigator service in Chicago where they figure out where he works/what he does when it's not for his business?