Scared and Confused

I'm new to this site, and joined so I could have someone to talk to about my situation. So my apologies for being lengthy.

I am just a few months away from marrying my best friend.  We both have known each other since we were 18 years old, and our lives finally came together nearly two decades later.  We have been dating for over two years now, and have been paying for and planning a big elaborate wedding set for this October.  

My fiance has been in law enforcement for 22 years and just got a promotion 5 months ago...which you all know follows with a new shift change in hours also.  Which means, he now works the late overnight shift.  That's where a majority of our problems began.   I am home alone at night while he is working and vice versa.   So our time spent together is limited.   And when we are together,  he needs his sleep.  All understandable, but it's very lonely.  

Our beginning happened when he sent me a message on messenger to see how I had been.  At that time, he was working the late shift,and talking to me at night while he worked. He was currently in a relationship and I was separated from my then husband, but still living in the same house,  different bedrooms.  It was nice friends chatter for a little bit, which he started flirting with me shortly after.   

I asked him if he was happy in his relationship,  and he told me he loved her very much and was very happy.  I asked why he was talking to me then...he replied with something  cute and said he just liked talking to me.   I was lonely at the time, and needed a friend.  But as the talking became more involved, I told him I didn't want to risk getting in trouble from my then abusive husband,  and told him I couldn't talk to him anymore.  He said he was devastated.   

Fast forward a few months.   I left my husband after I found out he cheated on me with a tinder hook up for a birthday present tto himself.   Got another message from my fiance who was just still my friend at that point, and we started talking.  He was broken up with his previous girlfriend, and now working daytime hours.  So we started spending time together.  And...being intimate, but not as a  couple. That lasted maybe two months,  and then he told me he needed to make things right with his previous girlfriend, and couldn't spend time with me anymore. 

That lasted two weeks.  He was back in my bed, and at times still with her.  And unfortunately, I accepted that. Primarily because I was lonely.  I still beat myself up over that to this day.

One month later...he was broken up with her, and we were official.  I announced it on Facebook, and his ex started sending me messages about how she found out he talked sex with multiple women.  I never responded to her, as she was in her own right a bit off from some of her actions. She stalked me until I had her blocked from everything.

Two happy years later, and one shift change, here we are 4 months out from being husband and wife.  BUT...things are not so happy.  

When the shift change happened,  so did the fights.  Intense fights, and the yelling.  And...my insecurities.   

He once told me the reason he talked to me while he dated her was because it was a toxic relationship.  And now, we are in a rough spot, and I wouldn't consider it toxic, but I'm not sure if he does or not.  

Ladies, I FEAR the possibility that hes talking to someone else, like he did with me.  We are not as intimate as we once were, and I cant tell you the last time he initiated sex with me.  I do all the initiating in that department.  

He continues to pay off this and that for the wedding, and has paid for nearly everything for it.  But while, my very sex driven fiance, is hardly intimate with me....he seems happy, when he can clearly see I am not so much right now.  I've told him I've been lonely, and he says hes not sure what he can do about it.  

His messenger activity was always very active, as it showed him on there nearly everyday,  always when we were apart.  I would confront him.about it, and it would start a fight.  I am not proud to admit that I have checked his phone a few times, and now, that app is not visible on his phone, but he still has it...somewhere, maybe hidden.  And when I did look, (I dont make it a habit) he had the private conversation turned on for it.  

It's all I can think about at nights when he gone. Is he having an affair while hes at work during the night? Is he talking to someone while hes bored sitting in his patrol car? He isnt needing sex from me...so where is he being satisfied?   I want more than anything to trust him, you have no idea. 

I love this man...but I am so scared,  and I just need some advice .