1) Good! Cheat! Don't take it too seriously man. One thing that shits me is people who micro manage their lives so fucking much. I just look at them and think bro, you're a) not lifting enough for all this shit to even be a factor. So I'm glad you're just chipping away at it and not letting it control you. GOOD MAN!
2) Over 50% of your weight is water, therefore any weight gained over half is water. That figure gets thrown around a lot I like to rule it off at 60% Lean muscle retains even more water. The bottom line is bro, lean muscle takes a long time to develop. You burn fat quicker than you gain muscle. From what you've told me so far, you're actually doing quite high volume exercises. I'm no expert but I'd say you're burning fat, drinking and eating plenty so you're well fueled. Any weight gain really is either going to be water/food or fat. Muscle makes up for a very small amount of out weight gains.
3) To explain this a little more. High volume training + cardio will do wonders for fat loss but very little for lean muscle development. You said it yourself you feel yourself getting leaner (less body fat) not larger!
4) 5x5 that's 5 reps by 5 sets for squats and 5x1 that's 5 reps by 1 set for deadlift. Try and get to a comfortable weight, I'm talking more in the low 100 range. I feel that you could be pushing yourself further with your squats and deadlifts. A good rule of thumb is to not combine them, or if you do only do one set of deadlifts. Deadlifts work more muscles than your other compound movements. This means it will tax your body more. Trust me bro, you're just going to tire yourself out. Being tired means you can't lift as much, if you can't lift as much it means you are not putting your muscles under the required trauma to properly develop.
Side note, it's great to hear that you are training for a triathlon!
A small suggestion for deadlifts would be something like this.
40 kilos for 5 reps
60 kilos for 5 reps
70 kilos for 5 reps
80 kilos for 3 reps
90 kilos for 3 reps
100 kilos for 3 reps
80 kilos to failure
Now this is just under 1.7 tonnes of total weight moved before you go crazy. You are getting the volume from the lighter weight but then are moving into triples at your current working weight and then overloading. After that drop down to 80 your current working weight and just destroy your legs. Go until you can't lift any more. Do this on like a Friday when you have the weekend to relax before starting again on Monday or when ever you can have the longest break. Give this a go for a few weeks
I haven't deadlifted since I failed twice on 180 two weeks ago, I've just been squatting. I have to thank stronglifts for getting me back into squats. I feel the best I've felt in these last two years. My legs feel fucking great.