Please don't mention your boyfriend or his schedule or the fact that you are reliant on someone else's schedule at all. It's an immediate and huge red flag that you might have difficulties getting to work on time. If you are applying for jobs that might have shifting schedules, it's an even bigger red flag.
Not saying that you, personally, will have trouble getting to work on time. But that's what it is going to seem like to a potential employer.
All you need to do is say that you need to check your calendar, take a quick look at your BF's schedule, and come back to say either the time and date are fine, or they aren't but give some days and times that are.
I've done a fair bit of hiring. Usually, I'd try to give the applicant a choice of two days/times. But even then, many couldn't make either appointment, and I'd just find another time to interview them.