I’ve been wondering if there’s an actual demon that can assure I and my girlfriend ( we are in a long distance relationship ) will meet this summer.
if your will is sufficient, you will find a way to see it. with demons you can change the situation or the experience with her more.
is there any demon I can summon?
make your point clear, is it just about meeting them?
meeting and spending some lovely time together
I guess that depends on how you want it to happen. Are you going to go to her and need to be well received? Are you asking her to come to you? What is the plan or what is in your imagination the best case scenario- that would then lead to questions about what is needed to make it happen- does one of you need money to do so, are there limitating thoughts and beliefs del either of you… and mostly what are her thoughts as far as wanting to see you as well.
we both want to meet like crazy in August. but her mom doesn’t trust me for some reason. And I’ll go to her place
regardless of whether you have been separated from her or just want to see her. just do it. I communicated before print out a seal from Lilith. think about what you really want and drop a drop of blood on you and touch it. close your eyes. not more.
The work with belial, dantalion, and paimon etc for building trust within the women and removing her limiting thoughts surrounding you.
Reach out to her mother and try to build a relationship of sorts in the meantime so that she comes along with basis that you are a good person on her own.
Look into practical djinn magic, goetia pathworking, or magic of influence by Corbin Hargrove- his books have rituals for gaining the trust of another person - both with demons and djinn and they are quite effective even for a newbie If you follow his process. He also has rituals for changing the mind of another etc.
Lady Beleth 
Lady Vual