Welcome momof3gr8boyz,
Your fears are normal (what ever that is) and reasonable.
Loosing your buddy on a dive never ever happens....well, OK, so it does happen and far too often. First start by agreeing before the dive what a dive buddy means and what is acceptable. Your lost contact may be another divers, "everything is fine, we are both still in the same ocean". So set the record straight before the dive and agree that a dive buddy can touch his/her dive buddy at all times. Each diver should approach the dive with "maintaining dive buddy contact is solely my responsibility" attitude. Get into the habit of looking at your buddy every 30 seconds or so. If one of the dive buddies is a photographer, put them in the lead as they will suddenly stop and go "ohhh pretty fishy" and promptly get lost in taking pictures and all too soon lost to their buddy too. Learn to recognize places or events that will cause buddy separation. If you are leading and go through a narrow place or have to slow down to negotiate a place, remember your buddy behind you will have to do the same thing, so wait on the other side for them. In limited visibility (and all other times too), keep your buddy in arms reach. In limited visibility sometimes you have to hold hands. If you stop to look at something, tap your buddy and show them too. But at the end, in limited visibility and good, you will from time to time loose your buddy. Have a pre-agreed dive buddy separation plan, search for one minute (stop, turn on your light which you carry day or night make two complete 360 revolutions waiving the flashlight up and down then back track for no more than 10 yards.). If you do not re-establish contact, then per your pre-agreed dive plan surface and stay there until your dive buddy surfaces.
Every diver should be a master at navigation. Make it a point even if someone else is leading the dive to always know where you are in the water and how to get back to the boat or beach. Some divers make the mistake of relying on their dive buddy for navigation, and then....buddyseperation or emergency, and it's how do I get back to safety? Or my favorite, we reach the turn and the dive leader points in the opposite direction as the way back. Know here you are in the water at all times. Practice navigation on shore by having a safety walk beside you (only to keep you from walking into a tree or hole) while you walk around the local park or large open field with a large towel or bag over your head so you can only see your feet and maybe 2 feet in front of your feet. Using only your dive compass navigate out 100 yards and back to the same location. Try a simple out and back, then a triangle pattern, then a rectangle pattern. You should come back to within say 6 feet of where you started. With practice you will get there. While on the dive, keep track by checking your compass and while you are at it, your gages every minute or so. You don't need to worry about 274 degrees for 10 minutes, just know you went west (just a tad north of west) for 10 minutes before turning due north for 15 minutes then East for 10 minutes and after that you will need...yes south for 15 minutes. That will get you in the right neighborhood. If there is a strong current on the first leg (always start the dive swimming into the current) remember the return leg will go faster if the current is still the same, to the east leg in the above example may become 9.5 minutes. With experience you will learn how to adjust. Best way to learn is to be the dive leader. Responsibility causes you to get good in a hurry. Tell your dive buddy to keep track too, but you do the navigation. Practice, Practice, Practice.
Mask coming off. 290 dives and I have not had it happen....yet. But it will. Try to keep you face out of your dive buddies fins. But from time to time you will wind up with fins in your face, turn your face away, raise an arm up in front of you to deflect fins. Other divers will cross over above you and kick you in the face with their fins (or worse). Just follow the above, and possibly carry a spare mask and try not to worry about it. It happens, but you are trained to deal with it.
With the exception of wrecks, most of the good stuff is above 60 feet anyway. So get into the water. You owe it to yourself and your body. SCUBA is an excellent aerobic exercise and promotes both excellent physical health, but mental health (OK, so we are all crazy) as well.