What to do about MIL? I don't want to hurt her feelings :/

cat • mama to 3 earthside, 2 angel babies. Pregnant with rainbow twins due April ‘25. 💜
So my boyfriend and I rarely have time to ourselves/go out on dates. I brought up to him going to the movies during the weekend and he thought it was a great idea. I was looking forward to having a little date night, going out to dinner and then the movies. I've been cooped up inside and just want to feel human again. Today his mother asked me if we saw the movie Suicide Squad yet and I said no, but that we plan to see it tomorrow. She was like oh what time are you going?? And I said I wasn't sure. She told me to let her know tomorrow so I'm guessing she wants to go.. 😔 I feel bad because I really just wanted it to be my boyfriend and I.. But today she cried infront of me telling me how unhappy she is and I feel sorry for her because she feels alone. Ugh 😕 she came with us the last two times because my boyfriend wanted to include her.. 😔 
Update: I talked to my boyfriend, I told him it's not like we don't invite her to stuff already... She's seen dead pool, and BvS with the both of us. and saw civil war with just him. She pretty much invited herself and then asked if it was okay... After the fact. We didn't have to heart to tell her no so it's whatever. 😐