How can I build a closer relationship with my new friend and stop our other friends from ruining it?

I need advice on a friend situation. Please bear with me on this one as it is quite a long story. I am in my senior year of high school and have recently became friends again with someone I was very close to in my freshman year and the first half of sophomore year, let's call him Alex. Alex and I drifted apart when I chose to leave the group of friends we shared. We have still spoke since then but not at all during vacations. However in September we started speaking more frequently and since the start of November our friendship has again flourished. Unfortunately we only have the opportunity to talk in school as we text sometimes but he is hopeless at answering his phone (I know he is not particularly ignoring me but I won't go into detail of this). We get on very well and have the exact same sense of humour but we can in other ways be opposite, he is very well liked and athletic but is not very confident where as I am more academic and confident but no where near as well liked as he is. I have found myself being much happier being closer to Alex again but there are a few issues.
The first: I feel that our friendship has recently gotten to a point where we are as close as we can be without having a closer relationship over social media or without socialising out of school (I am not sure what we could do and we live about 5 miles apart).
The second: my best friend of 5 years has gotten quite jealous over it. I am unable to discuss Alex with him and he has tried to talk to Alex more too. I have found that my friend sucks up to Alex a lot which is very annoying and I believe this is because he doesn't want Alex and I to be close, I don't know if Alex realises that my friend does this cause he can be quite blind to things like this. It's almost like if he can't be my best friend then no one else can. Now I do want to stay friends with him but I would love Alex to be my best friend in the future.
The third issue: alex and I started to get closer again when he also left the group we used to share. However, like with me when I left, they have been very desperate not to let him leave and are making much more of an effort with him now than they ever has. Now Alex does not want to remain in this group but he is more prone to giving in than I am, which I put down to his lack of confidence, so I believe they may be able to convince him to come back to them.
The fourth and final issue: Alex's childhood best friend. Ever since I have known Alex he has always been best friends with the same boy from when he was a child, let's call him Gary. Gary and I are good friends but we don't share as good a relationship as Alex and Gary do. They have a shared history and live very near each other so socialise out of school. Now Gary has his own friend group which he has tried very hard to get Alex involved in despite the fact that he does not want to be involved in. As I have previously mentioned Alex is very well liked so Gary's group would be happy to have him so I worry that he gives in too easily to Gary and joins his group.

Now here are the questions I need answered:
1. What can I do to build a social media friendship between Alex and I?
2. What can I do to stop my friend from getting in the way without him realising?
3. What can Alex and I do out of school to build our relationship (we live in an area of 6 towns pop. 40000 in all but a lot of the area has very bad poverty so there is not much to do)?
4. How can I encourage Alex not to go back to our old group or join Gary's group (I am definitely not being biased in saying he doesn't want to join these groups, it is just that he is not a confident person which I think is pretty self explanatory in this situation)?

Thank you for reading this and any serious and well thought out advice is welcome. I may seem obsessed but I am simply a very analytical person who likes to go through every situation with a fine tooth comb so possibly I am over thinking things. I have certainly noticed more about this than Alex has. Thank you again