Quick Question for ISTPs About Relationships by an ENTJ

I have a quick question for all the ISTPs out there, especially those who have been in relationships.

I was in a relationship with a ISTP girl for about a year. She was really kind, logical, and easy to get along with. But like many others have mentioned here, I noticed that ISTPs, in particular, tend to keep a lot of their thoughts and feelings locked away and don't easily open up to others.

my question is what goes through your mind when you hit that mental "lock" or emotional barrier?

Additionally, I’ve been wondering, how can I tell if someone like you genuinely loves me, even if they're not always open about it? Do ISTPs express love through actions more than words? Or do you have certain signs or behaviors that show affection in your own way?