Firstly you need to test various stages of network connections because network issues is the most common cause.
1. wifi to wifi in your property.
Have someone in your property use a computer to connect to the home's wifi and have them or you face time each other over wifi. Move the iphone around the property, the connection should be rock solid. If the connection drops or keeps dropping intermittently then you either have a hardware issue with the wifi box or the iphone is problem.
If the connection is rock solid and never drops then move to 2.
2. Wifi to your internet service provider.
Having iphone still on wifi, watch a video on youtube. If the connection keeps on dropping then there is an issue with your internet service provider.
If the connection never drops and there is no interuption in the video then move to 3.
3. Testing your mobile phone provider.
Take the iphone off wifi and connect it to the mobile network. Now watch the same video again. If the video keeps stopping for long periods or keeps starting then stopping then it shows there is problem with your mobile network provider.
If the video is stable and there is no interuptions or disconnections whilst watching the video then it's safe to say that everything is working ok on your end. Now you would need your BF to do exactly the same tests. If your BF tests come out the same as yours, basically no problems then it's down to two possible problems, if your both at home using wifi, you at your place and BF at their place when you face time then it could be the problem of your internet providers network communicating with one another. If your both using the mobile phone network then again it could be the problem of both mobile phone network providers communicatiing with one another.
There is a lot of network interference out there, even bad weather can cause network signals to drop, surges in electricity can affect network signals, electrical surges say from manufacturing buildings or a media event like a concert. Low flying planes and helicopters can disturb network signals. Poorly configured network substations or failing substations could be the problem.
This is why it is very important to do the home tests to eliminate if it's the iphones that are at fault.